JOURNAL OF TROPICAL PEDIATRICS, VOL. 57, NO. 6, 2011
A Comparison of Different Methods of Temperature
Measurements in Sick Newborns
by Sinan Uslu,1,2 Hamus Ozdemir,2 Ali Bulbul,1 Serdar Comert,1 Fatih Bolat,1 Emrah Can,1 and Asiye Nuhoglu1
1
Department of Pediatrics, Division of Neonatology, Sisli Etfal Children Hospital, Istanbul, Turkey
2
Department of Pediatrics, Division of Neonatology, Diyarbakir Children Hospital, Diyarbakir, Turkey
Correspondence: Sinan Uslu, Department of Pediatrics, Division of Neonatology, Darusafaka mah. Acelya sok. Yonca sit.
1B blok D:9 Istinye, 34460, Istanbul, Turkey; Sisli Etfal Children Hospital, Halaskargazi Cad. Sisli, 34360, Istanbul, Turkey.
Tel: þ90 532 737 00 15, Fax: þ90 212 234 11 21. E-mail: <[email protected]>.
Summary
We aimed to compare the accuracy of digital axillary thermometer (DAT), rectal glass mercury thermometer (RGMT), infrared tympanic thermometer (ITT) and infrared forehead skin thermometer (IFST)
measurements with traditional axillary glass mercury thermometer (AGMT) for intermittent temperature measurement in sick newborns. A prospective, descriptive and comparative study in which five
different types of thermometer readings were performed sequentially for 3 days. A total of 1989
measurements were collected from 663 newborns. DAT and ITT measurements correlated most closely
to AGMT (r ¼ 0.94). The correlation coefficent for IFST and RGMT were 0.74 and 0.87, respectively.
The mean differences for DAT, ITT, RGMT and IFST were þ0.02 C, þ0.03 C, þ0.25 C and
þ0.55 C, respectively. There were not any clinical differences (defined as a mean difference of
0.2 C) between both mean AGMT&DAT and AGMT&ITT measurements. Our study suggests that
tympanic thermometer measurement could be used as an acceptable and practical method for sick
newborn in neonatal units.
Key words: Temperature, newborn, thermometers, axillary, rectal, tympanic, digital, infrared.
Introduction
Maintainance and monitoring of the thermoregulation of newborn infants is a basic requirement of
good neonatal management and play a key role for
neonatal nursing care in the neonatal intensive care
unit (NICU). Determining accurate measurement of
temperature is very important because abnormal
temperature is strongly associated with a serious condition [1, 2]. Temperature of newborns may be measured in a variety of sites, including rectum, tympanic
membrane, forehead and axilla and using a number
of different tools, including glass mercury, digital,
electronic and infrared thermometers.
Temperature measurement by the axillary method
has become the accepted neonatal nursing care [3, 4].
Because of the greater surface vasculature, increased
body fat and thermal uniformity, temperature measured in the axillary area is considered reliable and is
used as a standard measurement site in newborns. No
significant differences have been noted between left
and right axillae [5].
Glass mercury thermometers are historically the
most acceptable standard methods of temperature
measurement. However, glass mercury thermometers
has some disadvantages such as danger of breakage,
potential harm and toxic vapor effects to health
workers and the patients. Therefore, glass mercury
thermometers are now used rarely in developed countries and studies are conducted to understand the efficacy of the various types of equipment available to
measure temperature [6].
The aim of this study was to compare the accuracy
of digital axillary thermometer (DAT), rectal glass
mercury thermometer (RGMT), infrared tympanic
thermometer (ITT) and infrared forehead skin
thermometer (IFST) measurements with traditional
axillary glass mercury thermometer (AGMT) for
intermittent temperature measurement in the NICU.
Methods
This study was performed between 1 December 2008
and 1 April 2009 in the NICU of the Diyarbakir
Children Hospital, in Turkey. During the study
period, the newborns who were hospitalized in
NICU of the Diyarbakir Children Hospital, were
included in the study. The patients with unstable conditions such as dysmorphic appearance, congenital
anomaly, septic shock and circulatory problem that
would effect measurement were excluded from
the trial. This was a prospective, descriptive and
The Author [2011]. Published by Oxford University Press. All rights reserved. For Permissions, please email: [email protected]
doi:10.1093/tropej/fmq120
Advance Access published on 18 January 2011
418
S. USLU ET AL.
comparative study in which three temperature readings were performed sequentially 3 days from each
newborn in incubator by the same neonatal nurse.
A health worker helped the nurse for stabilization
of the patients. Prior to the onset of data collection,
the data collector nurse was instructed for correct
temperature measurements procedures utilizing the
five methods. An oral informed and written consent
were obtained from the parents of the infants.
Temperature was measured using the following:
glass mercury thermomether (for axillary and rectal
tools separately), digital thermometer (Microlife
digital thermometer, model MT 3001, Microlife AG
Swiss Corp., Widnay, Switz), tympanic thermometer
(First Temp Genius, Tyco Healthcare Kendall,
Mansfield, Massachusetts) with disposable probe
covers and infrared skin thermometer (Thermoflash
LX-26, Visiomed France, Mountreuil, France).
The glass mercury thermometers and the tympanic
thermometer were supplied by hospital’s central service. The infrared skin thermometers and digital
thermometers were provided by the authors of the
study. The glass mercury thermometer (GMT) and
digital thermometer were used separately for each
patients.
Bilateral axillae were utilized for glass and digital
thermometers, and right ear was chosen for tympanic
thermometer. Infrared skin temperature was obtained on the central part of forehead. Axillary and
forehead region were dried using a towel before the
measurement. The GMT was shaken before using in
order to decrease the reading below 35 C. Infrared
skin thermometer was put in incubator or it was kept
at room temperature for 15 min before using. First,
digital and glass mercury thermometers were randomly placed in bilateral axillas separately in
supine position at the same time. Patients were stabilized by a health worker. Simultaneously tympanic
thermometer was inserted into the right external
auditory canal by pulling the pinna straight back
and the probe was directed toward the eye. The
prob was held in the ear canal until a beep was
heard. After this procedure according to principles
and precautions of manufacturer, infrared skin
thermometer readings were recorded three times by
placing the device approximately 5–15 cm above forehead skin (mean value was accepted). Immediately
after IFST measurement, a rectal glass thermometer
was inserted upwards to a depth of 3 cm in a term
and 2 cm in a preterm baby.
All the temperature measurements were recorded
in the morning between hours of 08:00 till 12:00
during the study period. The room air temperature
and relative humidity were kept constantly at
22–26 C and a relative humidity of 30–60%, respectively [7]. The temperatures of the incubators were
adjusted according to the standard temperature
reccommendations based on gestational age [8]. All
readings were done by celcius ( C) scale. A time of
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Vol. 57, No. 6
3 min was needed for axillary and 2 min for rectal
thermometer, approximately 1–3 min with digital
thermometer, 3 s with tympanic thermometer and
1 s with infrared skin thermometer. All measurements
were terminated nearly at 8–10 min.
Five temperature measurements were obtained by
data collector for each sample. Data analysis
included Pearson’s r coefficients (to determine the
strength of the correlation), paired t-tests (to determine statistically significant difference), standard deviation, mean and range using SPSS statistical
package. Scatter plot method was used in order to
compare axillary glass thermometer with every other
devices. Clinical signifance was defined as a mean
difference of 0.2 C between axillary glass temperature and other four measurements [9].
Results
During the study period, 742 patients were hospitalized in the NICU. Seventy nine neonates who met
the exclusion criteria were not included in the trial.
Six hundred sixty-three newborn infants were
included in this study and 1989 measurements of
data were used during statistical analysis. Three hundred and forty-one of them were males (51.4%) and
the average gestational age, birth weights and postnatal age during the study period were 36 3.6
weeks, 2468 11 g and 11 7.4 days, respectively.
Among the babies in the study group, 305 (46%)
were preterm whereas 358 (54%) term. The study
group did not include any postmature baby.
Among the babies, 319 (48.1%) were found to be
low birth weight (LBW) (<2500 g) whereas 344
(51.9%) had a birth weight 2500 g. The temperature
values of the patients and mean differences according
to gestational age (preterm and term) and birth
weight (<2500 g and 2500 g) were summarized in
Table 1. When all methods of temperature measurement were taken into consideration, any clinical difference which was defined as a mean difference of
0.2 C was not observed between patients regarding
gestational age and birth weight. The hospitalization
etiologies of patients in the study group were shown
in Table 2.
The correlation between five methods were given
in Table 3. DAT and ITT measurements correlated
most closely to AGMT (r ¼ 0.94). The correlation
coefficent for IFST and RGMT were 0.74 and 0.87,
respectively. The comparison of measurement of
DAT, IFST, RGMT and ITT with AGMT were
shown in Figs 1–4, respectively. The comparison of
the temperature readings done by AGMT and DAT,
and AGMT and ITT is seen in Figs 1 and 2, respectively. A significant correlation was found between
comparable methods (Fig. 1, Rsq 0.886, Fig. 2, Rsq
0.885). The comparison of AGMT and RGMT temperature measurements were shown in Fig. 3. There
is good correlation between these methods (Fig. 3,
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S. USLU ET AL.
TABLE 1
The temperature measurement of the patients according to gestational age (preterm and term) and
birth weight (<2500 g and 2500 g)
Types of
Thermometera
Gestational age
AGMT
DAT
ITT
RGMT
IFST
36.71 0.41
36.72 0.41
36.73 0.41
36.94 0.42
37.21 0.47
Birthweight
Preterm
babies (n ¼ 305)
Term babies
(n ¼ 358)
Mean
differenceb
<2500 g
(n ¼ 319)
2500 g
(n ¼ 344)
Mean
differenceb
36.76 0.41
36.77 0.40
36.78 0.41
36.98 0.41
37.24 0.48
0.05
0.05
0.05
0.04
0.03
36.70 0.40
36.72 0.40
36.72 0.41
36.94 0.41
37.21 0.48
36.77 0.41
36.78 0.41
36.80 0.41
36.99 0.42
37.23 0.48
0.07
0.06
0.08
0.05
0.02
a
Values were given as mean SD by celcius ( C) scale.
There were no clinical differences (defined as a mean difference of 0.2 C) between patients according to gestational age
(preterm and term) and birth weight (<2500 g and 2500 g).
b
TABLE 2
The hospitalization etiologies of patients in
the study group
Etiologies
Respiratory diseases
Perinatal asphyxia
Sepsis
Prematurity
Hyperbilirubinemia
Surgical diseases
Other diseases
TABLE 3
Correlation coefficents for temperature
measurements between axillary glass thermometer
and other four methods
Infants (n ¼ 663) n (%)
273
109
91
78
41
23
48
(41.2)
(16.4)
(13.7)
(11.8)
(6.2)
(3.5)
(7.2)
Types of
Thermometer
Pearson’s correlation
coefficents
AGMT
DAT
ITT
RGMT
IFST
1.0000
0.94
0.94
0.87
0.74
FIG. 1. Scatter plot of the difference between temperatures measured by AGMT and DAT.
FIG. 2. Scatter plot of the difference between temperatures measured by AGMT and ITT.
Rsq 0.758). Poor correlation between AGMT and
IFST temperature measurements is seen Fig. 4
(Rsq 0.596).
The mean temperature measurements were
given in Table 4. The DAT had the smallest range
(35.4–38.6 C). The IFST had the widest range
(35.9–39.6 C). Mean AGMT measurement (36.74 0.41 C) was compared with DAT (36.75 0.40 C),
ITT (36.76 0.42 C), RGMT (36.97 0.42 C) and
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S. USLU ET AL.
FIG. 3. Scatter plot of the difference between temperatures measured by AGMT and RGMT.
FIG. 4. Scatter plot of the difference between temperatures measured by AGMT and IFST.
TABLE 4
Measurement ranges of five methods
acquired infections [2, 6]. Therefore, several studies
have been conducted to determine the most accurate
and practical device.
Digital thermometers have been shown to be a
valuable method for neonatal temperature measurements. Sganga [6], Smith [11] and Leick-Rude et al.
[12] found that the digital thermometer had a high
correlation with the AGMT. In our study, the mean
difference between AGMT and DAT was statistically
significant, but not clinically significant. We demonstrated a good correlation between AGMT and
DAT.
ITT is useful for clinical temperature measurement
as long as moderately variability between patients is
acceptable [13]. There are studies supporting the use
of ITT among various age groups including newborns [14–16]. Weiss et al. [17] and Weiss [18]
found that mean ear and axillary temperatures were
highly correlated in newborns. However, its accuracy
has been questioned for newborns in some studies
[6, 19]. In our study, we found a high correlation
between AGMT and ITT measurements. Although
the mean difference of temperature measurements
was statistically significant, a clinical significance
was not found.
Rectal temperature measurement with glass mercury thermometer was reported to be the accurate
method compared with the axillary measurements
in newborns [20, 21]. Fulbrook et al. [22] stated
that rectal temperatures to be consistently higher
than temperatures taken at other sites possibly due
to increased metabolic activity or bacteria. Hissink
et al. [23] showed a wide variation of the mean difference between axillary and rectal temperature in
newborns. In a systematic review, Craig et al. [24]
concluded that the difference between temperature
reading at the axilla and rectum using glass mercury
Types of
Thermometer
Mean ( C)
Standard
deviation
Range ( C)
AGMT
DAT
ITT
RGMT
IFST
36.74
36.75
36.76
36.97
37.22
0.41
0.40
0.42
0.42
0.47
35.5–38.7
35.4–38.6
35.4–38.7
35.5–39.1
35.9–39.6
IFST (37.22 0.47 C). When we evaluated the correlation between AGMT and the other methods, the
mean differences for DAT, ITT, RGMT and IFST
were þ0.02 C, þ0.03 C, þ0.25 C and þ0.55 C,
respectively. The mean differences were significant
(p ¼ 0.001, p ¼ 0.001, p < 0.001, p < 0.001, respectively). But there were no clinical differences (defined as
a mean difference of 0.2 C) between mean AGMT
and DAT measurement, and mean AGMT and ITT
measurement.
Discussion
Accurate and practical temperature monitoring is
essential for clinical neonatal care and time management in neonatology units. Glass mercury thermometers and axillary region have been considered the
gold standard method of temperature measurement
in newborns [6, 10]. Although glass mercury thermometers have been used for a long period of time, this
procedure had also some important disadvantages
such as danger of breakage, potential harm and
toxic vapor effects; difficulties in reading the values
on the device; and possible role in spread of hospital
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S. USLU ET AL.
thermometer showed wide variation across studies.
Our study had same result also. There was a statistical and clinical significance between AGMT and
RGMT.
Kemp et al. [25] compared AGMT and infrared
axillary skin temperature and found good correlation
between two devices but the measurements were from
the different regions. Can et al. [26] concluded that
the noncontact infrared thermometer could not be
recommended for assessment of body temperature
in newborns admitted to NICU. Similarly, we
found a less correlation between AGMT and IFST
results. The mean difference of measurements was
significant both statistically and clinically.
According to our study results, IFST measurement
does not seem to be suitable and accurate for sick
newborns.
This study has some limitations. Measurements
were performed from the different body region by
the same neonatal nurse. Different body regions
have separate surface vasculature, metabolic activity
and body fat composition. This condition might
affect the measurements of the temperature.
However, Kunnel et al. [20] found no difference in
temperatures taken rectally, femorally, from the
axilla or skin. Another limitation of our study was
that we did not have a true measure of core body
temperature to use as a criterion standard. In the
literature, esophageal or pulmonary artery temperatures are generally considered to be true measures of
core body temperature [27]. But both methods are
invasive procedures.
The ideal measuring device should be a noninvasive, with a rapid result, accurate and practical to use.
We measured temperature using five different devices
and different sites in the same baby three times to
find an ideal tool. We found statistically significant
differences between measurements, but concluded
that the differences between AGMT and DAT or
ITT seen (0.01–0.02 C) were not clinically significant.
Both of them were noninvasive, but ITT had more
rapid results.
Conclusion
Good correlation with glass mercury thermometer,
rapid result delivery, improved patient comfort,
being an easy and noninvasive procedure and lacking
the disadvantages of glass mercury thermometer are
the advantages of tympanic thermometer. Our study
suggests that tympanic thermometer measurement
could be used as an acceptable method for sick newborns in the neonatal units.
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